The Effect of Fish Biomass and Denitrification on the Energy B

Problem: The Dutch aquaculture industry is based on fish production in recirculating aquaculture systems. Enforced by legislation the fish farmers have to reduce the waste discharge and are not allowed to discharge farm effluents on the surface waters. The government expresses waste discharge in inhabitant equivalents (I.E = average daily waste production of 1 person during 1 year, expressed in g O2 and measured as COD and Kjeldahl nitrogen) and charges levies between $ 29 and $ 60 per I.E. depending on the local water authority. In the near future, the government will impose stricter effluent and ground water permits and control procedures, which will force the farmers to invest in additional monitoring equipment and in waste water treatment. The latter may decrease the environmental load of a farm but may increase production costs considerably. Farm gate prices of African catfish are low and fluctuates around $1.50 per kg fish at an annual production of ±1000 kg/m tank volume and a water discharge of ± 100 l/kg feed per day. To create financial space for additional water treatment methods energy and production costs must be reduced further. The incorporation of denitrification may decrease the environmental load and energy costs for heating makeup water but can result in a demand for cooling during summer months.